The present invention relates to a method and apparatus for producing stereoscopic images.
The principle of stereoscopic vision is well understood. At the most basic level, each of the viewer's two eyes must perceive the subject matter to be viewed from a slightly different perspective. That is to say that, although the differences are generally quite subtle, each eye receives a different image.
Several methods are commonly used to produce stereoscopic images. On the one hand these include the use of direction selective screens onto which two or more images may be projected simultaneously. Depending on the viewer's position, a different image may be observed by each eye. Where only two images are required, it is common practice to use polarising techniques. Each image is projected with a characteristic polarisation and when viewing through complementary polarising viewing spectacles, each eye only sees the picture intended for its reception.
In television systems, it is possible to use projection techniques together with two or more complete display channels, typically one or more electronic display such as a Cathode Ray Tube (CRT) for each perspective to be displayed. However these systems tend to be costly because of the large amount of equipment needed. There may also be difficulty in obtaining proper alignment of the total system. In order to overcome the need for more than one image creation surface such as the phosphor coated screen of a colour CRT, anaglyph techniques have been used with some modest success. The anaglyph system, as practised in the current art, depends on the use of complementary colour filters placed in front of each eye. For example a red transmitting filter may be used for the left eye, and a blue and green transmitting filter used for the right eye. After each eye has become accustomed to the particular colour bias, and by displaying the left hand perspective of the subject in red and the right hand perspective in blue-green, a reasonable stereoscopic image may be observed. However, because each eye is observing a very restricted portion of the full colour spectrum, only limited colour information can be added to what generally appears as a lightly tinted picture.
A further proposal which has been made in the prior art is to produce on a screen full colour images of the left and right perspectives alternately. The screen is viewed through spectacles which permit each eye to receive only the image of the appropriate perspective. This system is described in, for example, U.S. Pat. Nos. 3,621,127 (Hope) and 4,021,846 (Roese) and in UK Pat. No. 1523436 (Mears). The problem with this system is that substantial flicker is produced because the image received by each eye alternates with periods of darkness.